Process of shortstopping polyolefinic compounds using alkali metal trithiocarbonate



United States Patent G PROCESS OF SHORTSTOPPING POLYOLEFINIC COMPOUNDS USING ALKALI METAL TRI- THIOCARBONATE Adolph J. Beber, Copley, Ohio, assignor to The General Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application October 8, 1953, Serial No. 385,035

12 Claims. (Cl. 26045.7)

This invention relates to the process of preventing further polymerization of polymeric organic compounds and particularly the preventing of undesired continued polymerization of polymers of diolefinic compounds such as the various synthetic rubbers after the desired state of polymerization has been reached.

In the preparation of organic compounds the monomeric materials are subjected to free radical initiators to cause them to build themselves into polymers of high molecular weight.

In many cases, it is desirable that polymer be stabilized against further change in characteristics. Unfortunately certain polymeric materials and particularly the solid polymeric diolefinic compounds which have substantial residual unsaturation tend to continue to polymerize after the desired polymer has been formed. The result is a hardening of the polymer and an increase in the amount of insoluble material or gel in the polymer.

In order to prevent the continued polymerization after the desired polymeric state has been obtained, it has been the customary practice to add to the latex of the polymeric material or to otherwise incorporate in the polymeric material an agent generally designated in the art as a shortstop which will inhibit further polymerization in the polymeric materials. Many so-called shortstops have been developed which were suitable for the shortstopping of rubbery materials polymerizable by the socalled hot recipes; i. e. those recipes which were highly active only at temperatures well above room temperatures. With the advent of the superior rubbers polymerized at temperatures well below room temperatures and generally at 50 F. or below, free radical initiator and activator systems were developed which were inefiectively shortstopped by the agents used for shortstopping the polymerization produced at elevated temperatures. Entirely new shortstopping agents, therefore, were required.

One of the earliest of these materials found to be effective was dimethylchlorobenzene. This material is troublesome because of its corrosive nature and causes severe dermatitis when it contacts the skin. It was subsequently found that certain of the dimethyldithiocarbamates such as the sodium and potassium dimethyldithiocarbamates were efiective shortstops for cold rubber.

It is an object of the present invention to produce shortstopping agents which are efifective for theprevention of polymerization of olefinic compounds beyond the desired state and which may be produced at less expense and with less difficulty than the alkali metal dimethyldithiocarbamates.

It is another object of the present invention to provide a process of shortstopping olefinic compounds to prevent the polymerization thereof beyond the desired state wherein a shortstopping agent, which is less expensive than shortstopping heretofore available and which is effective in relatively small amounts, is suitably incorporated into the polymeric material.

The above and other objects which will be apparent ice from the following description of the invention are obtained by incorporating into the mixture of polymeric material a relatively small amount of an alkali metal trithiocarbonate such as sodium, potassium, lithium or ammonium trithiocarbonate.

I have found that the trithiocarbonates and particularly the alkali metal trithiocarbonates are at least as efiective as the dithiocarbonates heretofore used in shortstopping the polymerization of olefinic (including diolefinic compounds) beyond the desired state. The alkali metal trithiocarbonates are more easily prepared and hence have the advantage of lower cost than the carbamates. We have found no evidence of dermatitis from the use of these compounds. When the materials are polymerized in the form of aqueous emulsion or dispersion as are the general purpose synthetic rubbers, they are preferably added to the latex immediately after the desired polymerization has occurred. The shortstopping agent may, however, be incorporated as a dry powder or as a slurry or as a solution into the polymeric material by any other method as by rolling on suitable mills or by means of a suitable mixer.

The alkali metal trithiocarbonates are effective shortstopping agents in extremely low percentages. I have found that as little as .05 based on the weight of the polymer of shortstopping agent greatly retards the rate of further polymerization and gel formation in polyolefinic compounds particularly the rubbery polymers of conjugated diolefinic compounds such as butadiene-l,3; isopropene; dimethyl butadiene; chloroprene; phenyl butadiene; cyanoprene; and other diolefinic compounds having double bonds in the conjugated relation and preferably having less than 7 aliphatic carbon atoms. When the amount of many shortstopping agent or agents is increased the resistance to continued polymerization is also increased. In most instances, it is desirable that the amount of shortstopping agent present he at least 0.1% of the weight of the polymeric material and that at least .05% total of at least one alkali metal trithiocarbonate be present.

It is preferred when the shortstopping is to be continued for substantial periods that the total amount of shortstopping agents present he at least 0.15 part based on the weight of the rubber. It is preferred that alkali metal trithiocarbonates be present in 0.15 alone such amount although mixtures of alkali metal trithiocarbonates with alkali metal dimethyldithiocarbamate may also be used advantageously. The upper limit of the amount of shortstopping agent incorporated in the polymer is limited only by economic considerations and generally does not exceed 2 or 3% up to 5% of the weight of the polymer.

The polymers to which the present invention is particularly applicable are the polymers of one or more diolefinic compounds of less than 7 aliphatic carbon atoms as aforementioned including the polymer and copolymer of butadiene-1,3, dimethylbutadiene, isoprene, cyanoprene, chloroprene, phenyl butadiene and the like having conjugated double bonds including the copolymers of one or more of the above diolefinic compounds with copolymerizable mono-olefinic compounds such as the various styrenes, including chlorostyrene, methylstyrenes, 3,4 dichloroalphamethylstyrene as well as methylisopropenyl ketone, acrylic and methacrylic acids, amides, nitriles and esters such as methylacrylate, methylmethacrylate, ethylmethacrylate, acrylo and methacrylo nitriles, and corresponding amides as well as other olefinic compounds copolymerizable with butadiene. The amount of diolefinic compounds in said polymers may be from about 1 or 2% to and is usually at least 15% and in most ub at as! %,;9?. aweishtqtmerchant,

The particular free radical type systems used in effecting polymerization is in accordance with the result of my experimental work, immaterial as the agents of the present invention are shortstops for the polymers produced by the various types, of free radical activated polymerization systems, of which I am aware. When, however, excessive amounts of free radical initiators are incorporated in the polymerization systems it is frequently desirable to add somewhat more of the shortstopping agent. Thus the present invention is eifective in shortstopping polymerization systems initiated by the combination of a peroxide or a hydroperoxide such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, sodium persul-fate, benzoyl peroxide, etc., with or without an amine such as triethylenetetramine and small amount of heavy metal salts such as versene (Fe-'3) or a cobaltic salt as well as a system initiated or catalized by peroxide in combination with sugars, sodium bisulfide or'other reducing agent with or Without a metal capable of existing in 2 valence states. Such systems are well known in the art and form no part of the present invention. The present invention is however, particularly effective in those polymerizations wherein the polymer is produced in aqueous emulsion.

The following examples in which parts are by weight illustrate the present invention.

EXAMPLE I A batch of butadiene-1,3 and styrene was polymerized Triton R-100 is a sodium salt of a complex, condensed organic acid. Versene Fe-3 is an organic complexing agent designed to form complex compound of hard-water salts, and divalentand trivalent metals, including iron, in the normal pH range of 3 to 12.5. It is widely used to form complex ions of harmful metals. Sulfole is a tert-dodecyl mercaptan; polymerization modifier obtained from Phillips Petroleum Company. Dresinate. 214. is a potassium soap of disproportioned rosin obtained from Hercules Powder Company.

The increment addition in the polyamine recipe was made after about conversion. The polymerization was allowed to progress sufiiciently to convert approximately of polymerizable monomers to the solid state. Each of the batches (A) and (B) of latices thus obtained were divided into several sub-batches. The batches from batch A being subdesignated as batch Al, A2, A3, A4, A5, A6, etc, and batch B being designated as B1, B2, B3, etc. The batches thus obtained were shortstopped at the end of the polymerization by the addition of the amounts and kind of shortstop indicated in the following table. They were then again incorporated into the polymerizer and subjected to further agitation. The total solids present were measured 4 hours later and 12 hours later. After 12 hours the various latices Were c0- agulated and the Mooney viscosity (ML-4) and percentat, 41 F. in accordance with each of the followlng g of gel measured 111 ch f th p e The results recipes: are shown in the following table:

TABLE I Parts of Short- Short- Solids Solids Solids Per- Batch stop (per 100 stop after after Change, MIL-4 cent 5. I. (1;)

of polymer) Solids, 4 hrs., 12 hrs., percent Gel percent percent percent 0.10 TTC. 22. 4 22.8 21. 7 0. 7 47 0 0 1. 22. 3 21. 8 21.3 1.0 42 0 0 1. 72 22.0 22.5 21.5 O. 5 49 0 0 1. 22. 4 22. 2 22.0 O. 5 57 0 0 2. 20 23.0 23.0 22.9 O. 1 52 0 0 2.01 23. 9 30. 7 34. 4 10. 5 66 55 1.05

Percent Percent Parts of Short- Short- '1. S. '1. S. Solids Per- Batch stop (per 100 stop after after Change, ML.4 cent S. I (1,)

of polymer) Solids, 4 hrs 8 more percent Gcl percent F hrs.,

20. 4 20.7 0. 3 102 0 0 3. 02 21.1 20.4 20.7 O. 4 1 90 0 0 3.02 21. 4 20.9 20.5 O. 9 1 81 0 0 2. 92 21.3 21.2 21. 3 0 1 76 0 0 2. 74 21.6 21.2 21.2 0. 4 1 71 0 0 2. 87 HQ, 21.5 22.3 20.9 0. 6 72 0 0 2.87 ortstop 20.9 31. 1 32. 5 11. 5 1 78 14 1. 07

l Tore on Mooney rotor.

TIO So dium trithiocarbonate. S DTC Sodium dimethyldithio carbamates. DN OB Dinitro chlorobenzcne.

Q=H droquinon e. 41 F. Recipes Batch A, Batch B, Iron-pyro- Polyamine phosphate Parts Parts- Butadiene 72. 0 72. 0 Styrene.-. 28.0 28.0 Dresinate 214... 2. 93 2.93 K-ORR Soa 1. 57 1. 57 N21 PO4-12Hz0. 0.5 0.5 Triton R100. 0.1 0.1 Sulfole B-S 0. 18 0. 18 Water 180.0 180. 0 Cumcnc hydroperoxide; 0. 15 0 Diisopropylbenzene hydroperoxule- 0 0, 11 Versene -Fe-3 0 0. 015 Triethylene tetramine 0 0,07 Sodium Sulfite 0 0. 35 K P2O1 0.27 0 FoSOyZHzO. 0.25 0 K. s 0.08 0 Diisopropylbenzene hydroperoxide (as mereruent 0 0. 064

Triethylene tetramine (as increment) 0 0, 04

It will be seen from the above table that the sodium trithiocarbonate is very effective in the prevention of gel and also in preventing increase in solids. The negative values for increase. in solids are within the scope of eX- perimental error.

EXAMPLE H A polymer was prepared at 122 F. using the following about 60% conversion as in. the previous example and .5 thereupon the shorstops indicated in the following table were added. Solids were measured 4 hours and 12 hours after the addition of shortstops to batches of the latex 6 thiooarbonate is incorporated into an aqueous dispersion of said polymer and the mixture thus formed is coagulated.

thus prepared as in the previous example. The results 3. A process of claim 2 wherein the alkali metal triare shown in the following Table II: 5 thiocarbonate is sodium trithiocarbonate.

TABLE II Percent Percent Parts of Solids Percent T. 8. after Solids Percent Shortstop Time of T. S. after 8more Change, ML-4' Gel S. I. (1

Short- 4 hrs. hrs. Percent stopping 1 Tore on Mooney rotor. PTO-Sodium trithiocarbonate. SDTO =Sod1um dimethyldlthiocarbamates. HQ=Hydroquinone.

It will be seen from the above table that sodium tri- 4. A process according to claim 1 wherein the amount thiocarbonate is just as effective as are the other shortof alkali metal trithiocarbonate present is .05 to of stopping agents at elevated temperatures. the weight of the polymer.

In the above examples other metal trithio- 5. The process of claim 1 wherein the polymer of a dicarbonates including ammonium trithiocarbonates, potasolefinic compound contains at least 1% by weight of the sium trithiocarbonates and lithium trithiocarbonates may residue from the polymerization of a conjugated diolefinic be substituted for all or part of the sodium trithiocarcompound of less than 7 aliphatic carbon atoms. bonate used. The alkali metal trithiocarbonates may also 6. The process for reducing the tendency toward furbe used in combination with other shortstopping agents ther polymerization of a copolymer of a diolefinic comsuch as hydroquinone and the alkali metal dimethyldipound of less than 7 aliphatic carbon atoms with a monothiocarbonates to give excellent results as aforementioned. olefinic compound copolymerizable therewith which com- The effect of the trithiocarbonate remains in the polyprises incorporating in said polymer .05% to 5% of an mer for a substantial period of time so that the further alkali metal trithiocarbonate. polymerization of the polymer is prevented even for sub- 7. A process according to the preceding claim wherestantial periods after the manufacture of articles from in the said copolymer is a polymer of butadiene-1,3 and the polymer. 7 a styrene.

While the present invention is primarily directed to the 8. A process according to claim 6 wherein the alleali preparation of rubbery polymers or polymers comprising metal trithiocarbonate is a sodium trithiocarbonate and a diolefinic compound such as a conjugated diolefine and wherein the polymer is a rubbery polymer of buta- Which are characterized by being vulcanizable it is also H ll applicable to the preparation of other unsaturated poly- 9. A polymer of a diolefinic compound comprising mers. .05% to about 3% of alkali metal trithiocarbonate.

It is to be understood that in accordance with the 10. A rubbery polymer of a diolefinic compound comprovisions of the patent statutes variations and modificaprising at least of said diolefinic comp having tions of the specific invention herein shown and described .05% to about 5% by weight of an alkali metal trithiomay be made without departing from the spirit of the carbonate'mixed therewith. invention. 11. A process according to claim 6 wherein the said What I claim is: 50 copolymer is a polymer of butadiene-1,3 and an acryloni- 1. A method of inhibiting further polymerization of trile. polymers of diolefinic compounds which comprises dis- 12. A process according to claim 6 wherein the said cotributing into the said polymer of a diolefinic compound polymer is a polymer of butadiene-1,3 and methylisopro- .05% to 5% based on the weight of said polymer of an penyl ketoim alkali metal trithiocarbonate.

2. A process according to claim 1 wherein the said tri- No references cited. 

1. A METHOD OF INHIBITING FURTHER POLYMERIZATION OF POLYMERS OF DIOLEFINIC COMPOUNDS WHICH COMPRISES DISTRIBUTING INTO THE SAID POLYMER OF A DIOLEFIN COMPOUND .05% TO 5% BASED ON THE WEIGHT OF SAID POLYMER OF AN ALKALI METAL TRITHIOCARBONATE. 